Well completions that produce hydrocarbons trapped in tight reservoirs are generally complex and expensive to install and maintain. In recognition of these complexities and expenses, added emphasis has been placed on efficiencies associated with these well completions and their maintenance over the life of the well.
It is commonplace for a well that produces hydrocarbons trapped in tight reservoirs to be partitioned into a number of intervals (also referred to as stages or zones) spaced along the length of the well. Short sections of unperforated production tubing (such as liner or casing sections) can be located between intervals to support isolation of the respective intervals. During well completion, hydraulic fracturing operations can be carried out over the intervals of the well. The hydraulic fracturing operations direct fracturing fluid under high pressure through fracturing sleeves or liner/casing perforations into the adjacent formation, which causes fracturing of the reservoir rock of the adjacent formation that is intended to release oil or gas trapped in the reservoir rock such that it flows into the well for easier production. The fracturing fluid typically contains a proppant (such as sand) that aids in holding the fractures open after the fracturing application has been completed.
Note that not all intervals of the well can contribute equally to the production of hydrocarbons from the well as the petrophysical and geomechanical properties of the reservoir can vary along the length of the well. Current workflows used to evaluate the productivity of individual intervals of the well are based on two main techniques. The first technique, commonly described as production logging, is based on the downhole measurements of fluid rates using spinners and pressure measurement. This first technique requires a production logging tool to be run in the well, thus increasing the cost of the well. The second technique is based on the measurement of tracer concentration. Different tracers are injected into the reservoir with the fracturing fluid over the intervals of the well. The tracers are produced from well with the fracturing fluid and/or hydrocarbons during the initial production of the well. The amount of each given tracer that is produced is a function of the flow contribution of the respective interval in which the given tracer was placed. The use of the multiple different tracers allows for the evaluation of the flow contributions over the number of intervals of the well. Beyond the limitation inherent to the interpretation of the produced fluids (including the tracers, the fracturing fluid and/or hydrocarbons), this second technique has a limitation in the number of tracers that can be placed into the intervals of a single well as well as the detection of the tracers in the produced fluids.